Realtime assessment of vascular occlusion and reperfusion in animal models of intraoperative imaging - a pilot study.

Objectives: Intraoperative monitoring of blood flow (BF) remains vital to guiding surgical decisions. Here, we report the use of SurgeON™ Blood Flow Monitor (BFM), a prototype system that attaches to surgical microscopes and implements laser speckle contrast imaging (LSCI) to noninvasively obtain and present vascular BF information in real-time within the microscope's eyepiece.

Methods: The ability of SurgeON BFM to monitor BF status during reversible vascular occlusion procedures was investigated in two large animal models: occlusion of saphenous veins in six NZW rabbit hindlimbs and clipping of middle cerebral artery (MCA) branches in four Dorset sheep brain hemispheres.

Determinants of acute irreversible electroporation lesion characteristics after pulsed field ablation: the role of voltage, contact, and adipose interference.

Aims: Pulsed field ablation (PFA) is a non-thermal ablative approach in which cardiomyocyte death is obtained through irreversible electroporation (IRE). Data correlating the biophysical characteristics of IRE and lesion characteristics are limited. The aim of this study was to assess the effect of different procedural parameters [voltage, number of cycles (NoCs), and contact] on lesion characteristics in a vegetal and animal model for IRE.

Real-Time High-Resolution MRI Endoscopy at up to 10 Frames per Second.

. Atherosclerosis is a leading cause of mortality and morbidity. Optical endoscopy, ultrasound, and X-ray offer minimally invasive imaging assessments but have limited sensitivity for characterizing disease and therapeutic response.

High-resolution intravascular MRI-guided perivascular ultrasound ablation.

Purpose: To develop and test in animal studies ex vivo and in vivo, an intravascular (IV) MRI-guided high-intensity focused ultrasound (HIFU) ablation method for targeting perivascular pathology with minimal injury to the vessel wall.

Methods: IV-MRI antennas were combined with 2- to 4-mm diameter water-cooled IV-ultrasound ablation catheters for IV-MRI on a 3T clinical MRI scanner. A software interface was developed for monitoring thermal dose with real-time MRI thermometry, and an MRI-guided ablation protocol developed by repeat testing on muscle and liver tissue ex vivo.

A Combined Intravascular MRI Endoscope and Intravascular Ultrasound (IVUS) Transducer for High-Resolution Image-Guided Ablation.

An intravascular MRI (IMRI) loopless antenna is combined for the first time with an intravascular water-cooled ultrasound ablation transducer as a possible tool for providing high-resolution MRI-guided ablations of pathological tissue via intravascular access. High resolution anatomical MRI, and real-time MRI thermometry were used to monitor ablation delivery in phantoms and tissue specimens. Results show that IMRI can guide IVUS-mediated directional ablation with minimal image artifacts.

Real-time magnetic resonance imaging guidance improves the diagnostic yield of endomyocardial biopsy.

Background: Diagnostic yield of endomyocardial biopsy is low, particularly in disease that affects the myocardium in a non-uniform distribution. We hypothesized that real-time MRI guidance could improve the yield through targeted biopsy of focal myocardial pathology.

Methods: An animal model of focal myocardial pathology was created by infusing 3mL of fluorescent microspheres (NuFlow Hydrocoat, 15μm diameter, 5 million spheres/mL) followed by 2mL of 100% ethanol to a branch coronary artery.

Designing passive MRI-safe implantable conducting leads with electrodes.

Purpose: The presence of implanted electronic devices with conducting leads and electrodes are contraindicated for magnetic resonance imaging (MRI), denying many patients its potential benefits. The prime concern is MRI's radio frequency (RF) fields, which can cause elevated local specific absorption rates (SARs) and potential heat injury. The purpose of this article is to develop and compare a range of passive implantable "MRI-safe" lead designs.

Intracoronary MR imaging using a 0.014-inch MR imaging-guidewire: toward MRI-guided coronary interventions.

Purpose: To validate the feasibility of using a newly designed MR imaging-guidewire (MRIG) to guide angioplasty balloon placement in coronary arteries.

Materials And Methods: A custom gold/sliver/Nitinol/MP35N-based, 0.014-inch MRIG was manufactured.

Minimizing RF heating of conducting wires in MRI.

Performing interventions using long conducting wires in MRI introduces the risk of focal RF heating at the wire tip. Comprehensive EM simulations are combined with carefully measured experimental data to show that method-of-moments EM field modeling coupled with heat transfer modeling can adequately predict RF heating with wires partially inserted into the patient-mimicking phantom. The effects of total wire length, inserted length, wire position in the phantom, phantom position in the scanner, and phantom size are examined.

Interventional cardiovascular procedures guided by real-time MR imaging: an interactive interface using multiple slices, adaptive projection modes and live 3D renderings.

Purpose: To develop and test a novel interactive real-time MRI environment that facilitates image-guided cardiovascular interventions.

Materials And Methods: Color highlighting of device-mounted receiver coils, accelerated imaging of multiple slices, adaptive projection modes, live three-dimensional (3D) renderings and other interactive features were utilized to enhance navigation of devices and targeting of tissue.

Results: Images are shown from several catheter-based interventional procedures performed in swine that benefit from this custom interventional MRI interface.

Magnetic resonance-guided, real-time targeted delivery and imaging of magnetocapsules immunoprotecting pancreatic islet cells.

In type I diabetes mellitus, islet transplantation provides a moment-to-moment fine regulation of insulin. Success rates vary widely, however, necessitating suitable methods to monitor islet delivery, engraftment and survival. Here magnetic resonance-trackable magnetocapsules have been used simultaneously to immunoprotect pancreatic beta-cells and to monitor, non-invasively in real-time, hepatic delivery and engraftment by magnetic resonance imaging (MRI).

Tracking planar orientations of active MRI needles.

Purpose: To determine and track the planar orientation of active interventional devices without using localizing RF microcoils.

Materials And Methods: An image-based tracking method that determines a device's orientation using projection images was developed. An automated and a manual detection scheme were implemented.

Beating heart aortic valve replacement using real-time MRI guidance.

Objective: : The principal limitations of percutaneous techniques to replace the aortic valve are detailed visualization and durable prostheses. We report the feasibility of using real-time magnetic resonance imaging (MRI) to provide precise anatomic detail and visual feedback to implant a proven bioprosthesis.

Methods: : Twelve domestic pigs were anesthetized, and, through a minimally invasive approach using real-time MRI guidance, underwent aortic valve replacement.

Evaluation of MR/fluoroscopy-guided portosystemic shunt creation in a swine model.

Purpose: To evaluate three different percutaneous portosystemic shunts created with magnetic resonance (MR) imaging and fluoroscopy guidance in a swine model.

Materials And Methods: In stage 1 of the experiment, an active MR intravascular needle system was created for needle tracking and extracaval punctures. Twenty inferior vena cava (IVC)/superior mesenteric vein (SMV)/portal vein (PV) punctures were performed in 10 swine (weight, 40-45 kg) in a 1.

Real-time MRI guided atrial septal puncture and balloon septostomy in swine.

Cardiac perforation during atrial septal puncture (ASP) might be avoided by improved image guidance. X-ray fluoroscopy (XRF), which guides ASP, visualizes tissue poorly and does not convey depth information. Ultrasound is limited by device shadows and constrained imaging windows.

Real-time magnetic resonance imaging-guided endovascular recanalization of chronic total arterial occlusion in a swine model.

Background: Endovascular recanalization (guidewire traversal) of peripheral artery chronic total occlusion (CTO) can be challenging. X-ray angiography resolves CTO poorly. Virtually "blind" device advancement during x-ray-guided interventions can lead to procedure failure, perforation, and hemorrhage.

Percutaneous MR imaging-guided transvascular access of mesenteric venous system: study in swine model.

Purpose: To determine if, with use of magnetic resonance (MR) imaging guidance alone, transcaval puncture of the superior mesenteric vein (SMV) and/or portal vein is feasible with a percutaneous femoral vein approach.

Materials And Methods: The Institutional Animal Care and Use Committee approved the animal studies. Ten inferior vena cava (IVC)-SMV punctures were performed in six pigs.

Simultaneous radiofrequency (RF) heating and magnetic resonance (MR) thermal mapping using an intravascular MR imaging/RF heating system.

Previous studies have confirmed the possibility of using an intravascular MR imaging guidewire (MRIG) as a heating source to enhance vascular gene transfection/expression. This motivated us to develop a new intravascular system that can perform MR imaging, radiofrequncy (RF) heating, and MR temperature monitoring simultaneously in an MR scanner. To validate this concept, a series of mathematical simulations of RF power loss along a 0.

Real-time magnetic resonance-guided endovascular repair of experimental abdominal aortic aneurysm in swine.

Objectives: This study tested the hypotheses that endografts can be visualized and navigated in vivo solely under real-time magnetic resonance imaging (rtMRI) guidance to repair experimental abdominal aortic aneurysms (AAA) in swine, and that MRI can provide immediate assessment of endograft apposition and aneurysm exclusion.

Background: Endovascular repair for AAA is limited by endoleak caused by inflow or outflow malapposition. The ability of rtMRI to image soft tissue and flow may improve on X-ray guidance of this procedure.

Development of a 0.014-inch magnetic resonance imaging guidewire.

The purpose of this study was to develop a standard 0.014-inch intravascular magnetic resonance imaging guidewire (MRIG), a coaxial cable with an extension of the inner conductor, specifically designed for use in the small vessels. After a theoretical analysis, the 0.

Magnetic resonance image-guided trans-septal puncture in a swine heart.

Purpose: To test the feasibility of performing magnetic resonance (MR)-guided trans-septal punctures in the swine heart.

Materials And Methods: All procedures were performed in a 1.5-T MR scanner.